1. Field of the Invention
This invention relates to an electroluminescent display device manufacturing method, particularly to an electroluminescent display device manufacturing method including a step of forming letters or symbols on a device substrate by applying laser beams.
2. Description of the Related Art
In recent years, electroluminescent (hereafter, referred to as EL) display devices with EL elements have been receiving an attention as a display device substituting for a CRT and an LCD.
Hereafter, there is described an example of a structure of a pixel of an organic EL display device.
FIG. 6 is a plane view showing a pixel of an organic EL display device. FIG. 7A is a cross-sectional view along A—A line of FIG. 6 and FIG. 7B is a cross-sectional view along B—B line of FIG. 6.
As shown in FIG. 6, and FIGS. 7A and 7B, a pixel 115 is formed in a region enclosed with a gate signal line 51 and a drain signal line 52. A plurality of the pixels 115 are disposed in a matrix.
There are disposed in the pixel 115 an organic EL element 60 as a self-emission device, a switching TFT (thin film transistor) 30 for controlling a timing of supplying an electric current to the organic EL element 60, a driving TFT 40 for supplying an electric current to the organic EL element 60 and a storage capacitor. The organic EL element 60 is formed of an anode 61, an emissive made of an emission material, and a cathode 63.
The switching TFT 30 is provided in a periphery of a point of intersection of the both signal lines 51 and 52. A source 33s of the switching TFT 30 serves as a capacitor electrode 55 for forming a capacitor with a storage capacitor electrode line 54 and is connected to a gate electrode 41 of the driving TFT 40. A source 43s of the driving TFT 40 is connected to the anode 61 of the organic EL element 60, while a drain 43d is connected to a driving source line 53 as a current source to be supplied to the organic EL element 60.
The storage capacitor electrode line 54 is disposed in parallel with the gate signal line 51. The storage capacitor electrode line 54 is made of Cr (chromium) or the like and forms a capacitor by storing an electric charge with the capacitor electrode 55 connected to the source 33s of the TFT through a gate insulating film 12. A storage capacitor 56 is provided for storing voltage applied to the gate electrode 41 of the driving TFT 40.
As shown in FIGS. 7A and 7B, the organic EL display device is formed by laminating the TFTs and the organic EL element sequentially on a substrate 10 such as a substrate made of a glass or a synthetic resin, a conductive substrate, or a semiconductor substrate. When using a conductive substrate or a semiconductor substrate as the substrate 10, however, an insulating film such as SiO2 or SiNx is formed on the substrate 10, and then the switching TFT 30, the driving TFT 40 and the organic EL element 60 are formed thereon. Each of the two TFTs has a so-called top gate structure in which a gate electrode is disposed above an active layer with a gate insulating film being interposed therebetween.
There will be described the switching TFT 30 first. As shown in FIG. 7A, an amorphous silicon film (hereafter, referred to as an a-Si film) is formed on the insulating substrate 10 made of a silica glass, a non-alkali glass or the like by a CVD method etc. The a-Si film is irradiated with laser beams for melting and recrystalizing to form a polysilicon film (hereafter, referred to as a p-Si film) as an active layer 33. On the active layer 33, a single-layer or a multi-layer of an SiO2 film and an SiNx film is formed as the gate insulating film 12. There are disposed on the gate insulating film 12 the gate signal line 51 made of metal having a high melting point such as Cr and Mo (molybdenum) and also serving as a gate electrode 31, the drain signal line 52 made of Al (aluminum), and the driving source line 53 made of Al and serving as a driving source of the organic EL element.
An interlayer insulating film 15 laminated with an SiO2 film, an SiNx film and an SiO2 film sequentially is formed on whole surfaces of the gate insulating film 12 and the active layer 33. There is provided a drain electrode 36 by filling metal such as Al in a contact hole provided correspondingly to a drain 33d. Furthermore, a planarization insulation film 17 for planarizing a surface which is made of organic resin is formed on the whole surface.
Next, there will be described the driving TFT 40 of the organic EL element. As shown in FIG. 7B, an active layer 43 formed by poly-crystalizing an a-Si film by applying laser beams thereto, the gate insulating film 12, and the gate electrode 41 made of metal having a high melting point such as Cr or Mo are formed sequentially on the insulating substrate 10 made of a silica glass, a non-alkali glass or the like. There are provided in the active layer 43 a channel 43c, and a source 43s and a drain 43d on both sides of the channel 43c. 
The interlayer insulating film 15 laminated with an SiO2 film, an SiNx film and an SiO2 film sequentially is formed on the whole surface of the gate insulating film 12 and the active layer 43. There is disposed the driving source line 53 connected to a driving source by filling metal such as Al in a contact hole provided correspondingly to a drain 43d. Furthermore, a planarization insulation film 17 for planarizing the surface, which is made of, for example, an organic resin is formed on a whole surface.
A contact hole is formed in a position corresponding to a source 43s in the planarization insulation film 17. There is formed on the planarization insulation film 17 a transparent electrode made of ITO (indium tin oxide) and contacting to the source 43s through the contact hole, i.e., the anode 61 of the organic EL element. The anode 61 is formed in each of the pixels, being isolated as an island.
The organic EL element 60 includes the anode 61 made of a transparent electrode such as ITO, a first hole transport layer made of MTDATA (4,4-bis (3-methylphenylphenylamino) biphenyl), a hole transport layer 62 made of a second hole transport layer made of TPD (4,4,4-tris (3-methylphenylphenylamino) triphenylanine), an emissive 63 made of Bebq2 (bis(10-hydroxybenzo[h]quinolinato)beryllium) containing a quinacridone derivative, an electron transport layer 64 made of Bebq2, and a cathode 65 made of magnesium-indium alloy, aluminum or aluminum alloy.
In the organic EL element 60, a hole injected from the anode 61 and an electron injected from the cathode 65 are recombined in the emissive and an exciton is formed by exciting an organic module forming the emissive 63. Light is emitted from the emissive 63 in a process of relaxation of the exciton and then released outside after going through the transparent anode 61 and the transparent insulating substrate 10.
In the organic EL display device having the above-described structure, for example, as shown in FIG. 8, a plurality of organic EL display units 201 are formed in a matrix at predetermined intervals on a glass substrate 200 called a mother glass. In the example of FIG. 8, four by four pieces of the organic EL display units 201 are formed. There is formed adjacent each of the organic EL display units 201, a numbering region 202 for forming letters, symbols, or the like (referred to as graphical symbols, hereinafter) which represent manufacturing information such as a manufacturing number or a lot number of the organic EL display unit 201.
FIG. 9 shows a method of forming graphical symbols on the numbering region 202 and corresponds to a cross-sectional view along A—A line in FIG. 8. There is formed on the glass substrate 200 the numbering region 202 made of Cr layer with an insulating film 120 interposed therebetween.
The insulating film 120 and the numbering region 202 are formed by utilizing a part of a manufacturing step of the above-described organic EL display unit 201. For example, the insulating film 120 is formed in a step of forming the gate insulating film 12 of the TFTs 30 and 40, and the numbering region 202 is formed in a step of forming the gate electrodes 31 and 41 of the TFTs 30 and 40.
Graphical symbols are formed on the numbering region 202 by scratching a surface of the numbering region 202 by applying laser beams 300 thereto.
After subsequent manufacturing steps, the organic EL display units 201 are completed forming on the glass substrate 200. The glass substrate 200 is then attached to a sealing substrate (not shown) with a sealing resin interposed between the substrates. Furthermore, the attached glass substrate 200 and sealing substrate are cut off to be divided in into individual organic EL panels.
In the step of forming graphical symbols on the numbering region 202 by the application of the laser beams 300, however, powders substances scattered by the irradiating laser beams adhere to the surface of the glass substrate 200 on which the device elements such as the TFTs and the organic EL elements are formed. This results in failure of the completed EL display device.